1. Field of the Invention
The present invention is related to a process for fabricating a surface-emitting laser diode with a metal reflector. Especially, it is related to the use of a combination of a metal reflector and wafer bonding technology to replace traditional epiwafer process or high-temperature high-pressure wafer bonding technology in fabricating VCSEL Bragg Reflector.
2. Description of the Prior Art
Take 1.3 or 1.55 xcexcm VCSEL as an example. Since traditional Surface-Emitting Laser diode has a kind of structure that the resonant cavity of the component is perpendicular to the epitaxial wafer layer with the reflective surface being composed of epiwafer layers or surface dielectric thin films and the laser is emitted from the front side, it is also called Vertical-Cavity Surface-Emitting Laser (VCSEL). The traditional technology continues to attract attention from worldwide research organizations since it was introduced to the world. In consideration of VCSEL components of various wavelengths, the development for VCSEL diodes of long wavelength (1.3 or 1.55 mm) still falls behind the development for those of short wavelength like VCSEL components of GaAs/AlGaAs series. It is found that the core of VCSEL is the resonant cavity, which uses Distributed Bragg Reflector (DBR) of epiwafer thin film that directly grows up and down the active region. Besides the structure and the characteristic of the active region, DBR reflectance and thermal conductivity also play critical roles in affecting the quality of VCSEL components. To reach such a high reflectivity, it relies on a proper match of the refractive index difference (xcex94n) and the number of reflector pairs composing DBR. For 1.3 or 1.55 mm VCSEL components, if lattice match is considered, only the active layer of InGaAsP/InP reflector grown on InP series can be selected. But InGaAsP/InP reflector pairs not only have poor thermal conductivity but also small refractive index difference An (compared to Gas/AlAs Bragg mirror), so a significant number of reflector pairs are required to increase reflectivity. Nevertheless, this gives rise to another problem that a tough challenge happens to the people carrying out epitaxial growth and a serious setback for production cost and yield also occurs because more than a thousand times of changes in molecular beams (MBE) or gas sources (MOCVD) and a very long growth period (4 to 8 hours) is required along with maintaining a growth error of less than 1% in such a complicated process of epitaxial structure growth. If a metal reflector of high reflectivity is made on a proper substrate (good heat dissipation and matched thermal expansion coefficients and active layers)with the use of wafer bonding technology to form an integrated laser active layer, the coated film quality of metal reflector will become easier to control than that of DBR epiwafer, and the cost will be reduced so that high quality VCSEL is easier to be produced.
As shown by the above description, the traditional technology still has many shortcomings, so it needs immediate improvement.
Seeing that the traditional technology mentioned above gives rise to many shortcomings, the inventor is eager to seek improvements and innovations. After many years of dedication to research and development, the inventor successfully invented a method for fabricating a surface-emitting laser diode with a metal reflector.
The objective of the present invention is to provide a method for fabricating a surface-emitting laser diode with a metal reflector, which uses wafer fusion technology to bond a metal layer of high reflectivity to 1.3 or 1.55 mm VCSEL structure to replace traditional lattice matched InGaAsP/InP DBR or uses crystal lattice of wafer fusion technology and 1.3 or 1.55 mm VCSEL unmatched GaAs/AlGaAs to form DBR. Another objective of the present invention is to provide a method for fabricating a surface-emitting laser diode with a metal reflector, which uses a metal reflector in accordance with wafer bonding technology so that the advantages include simple process, low production cost and good VCSEL characteristics etc.
The methods to achieve the above-mentioned objectives of fabricating a surface-emitting laser diode with a metal reflector include: a substrate of metal reflector structure, a substrate of epiwafer film with surface-emitting laser structure, wafer bonding technology and epiwafer film removal technology. Wafer bonding is used to combine the epitaxial VCSEL wafer of active region and the wafer of top and bottom reflectors, followed by high-temperature, high-pressure and substrate removal procedures to form VCSEL. The metal reflector structure is made of materials like Au, AuBe, AuZn, AuGeNi, AuGe, Ni, Pt, Ti, TiN, Ta, TaN and Pd in layer of a single kind of metal or in multiple layers of metals. Surface-emitting laser diode can emit laser of wavelengths at 850, 1300 and 1500 nm. The laser diode can be produced by metal organic chemical vapor deposition or molecular beam epitaxial growth.